Milling cutters are commonly used for profile and cavity milling in the auto, aircraft, die and mold industries, and in general manufacturing. In particular, the milling tools are used for profiling or copy milling for rapid prototyping. Plastic, non-ferrous, and ferrous materials are precisely milled using milling tools. Smooth blending and finishing of three-dimensional curves and shapes with software-generated tool paths is also accomplished. Cavity milling methods include roughing, finishing, spiral pocketing, Z-level milling, fillet and pencil tracing and cusp removing. As shown in FIGS. 17-19, milling cutters 10 can be used for step-over line milling, as shown in FIG. 17, side milling on steep walls as shown in FIG. 18, and corner radius milling as shown in FIG. 19. Modern milling cutters often include a tool holder and a replaceable cutting tool insert. The tool holder supports the cutting tool insert as the tool holder is rotated about its central longitudinal axis and the cutting tool insert is provided with a cutting surface for milling plastic, non-ferrous, and ferrous materials.
A problem with conventional milling cutters utilizing replaceable cutting inserts is that the cutting tool inserts are commonly not sufficiently supported by the tool holder. It is also difficult to ensure that the cutting tool insert is on a true center-line when put to use in its cutting mode. Thus, it is desirable in the art of milling cutters to provide a tool holder and cutting tool insert design which improves the tool holder's ability to properly support the tool insert under cutting loads.
A three axis milling machine is the most common machine for tool making, therefore the most widely used cutting tool insert for tool making is a ball nose insert. A ball nose insert, as shown in FIG. 17, has a semi-circular cutting edge. The ball nose insert can be used to manufacture sculpted surfaces with a three axis machine, including convex or concave shapes, quite accurately and economically. However, a ball nose insert has several distinct disadvantages. The cutting speed of a ball nose insert changes constantly along the cutting edge. The cutting speed of a ball nose insert is zero at the tool tip and reaches its maximum at the outer diameter of the tool. Because the cutting speed is zero at the tool tip, the resulting cutting surface has a duller appearance and a rougher surface. Furthermore, a zero surface speed at the tool tip results in faster tool wear and chipping or breaking of the cutting edge of the insert. A toroid cutting tool, as shown in FIG. 20, solves some of the problems encountered when using a ball nose insert. There is no area on the cutting edge of a toroid cutting tool where the cutting speed is zero. Furthermore, toroid cutters do not require the higher spindle speed requirements of a ball nose insert. However, there are also disadvantages with conventional toroid cutters. Conventional toroid cutters generally include two or more interchangeable inserts known as button inserts, which are held in place by a screw or a clamping finger. It is difficult to manufacture the inserts to tolerances that assure, as inserts are replaced, that a cutter with precise, repeatable cutting geometry will result. Repeatable cutting geometry allows metal removal that is equal in volume from one cutting edge to the next cutting edge, resulting in a balanced cutting action. Thus, it is desirable in the art of milling cutters to provide a cutting tool insert design which improves the quality of the cutting surface of a workpiece while also increasing the accuracy and efficiency of a machining operation.